The present invention relates to a printing plate and a process for plate-making.
Photo-sensitive or heat-sensitive printing plates are known. The photo-sensitive plate is processed for plate-making by selectively irradiating the plate to vary the physical properties of light-irradiated portions and non-light irradiated portions and by taking advantage of the differences in the hydrophilic and lipophilic properties of light polymeric substances, the solubilities of their solvents, electrifying properties of photo-conductive substances and the adhesive strength of the light degradative substances. The heat-sensitive plate is processed by selectively applying heat to the plate to vary the physical properties of the heated and non-heated portions and by taking advantage of the differences in adhesiveness of the heat-sensitive material, the differences between hydrophilic and lipophilic properties, or the differences in perforating property of the heat-sensitive film.
These processes for plate-making, however, require an expensive plate-making apparatus hardly used in any other processes than plate-making, and there was such a problem that the process is complicated and the printing plate cannot simply be made.
Japanese patent application laid-open No. Sho 61-12387 discloses a process for plate-making by dissolving a printing plate having a water-insoluble resin layer with a resin-soluble solvent and Japanese patent application laid-open No. Sho 59-67051 discloses a process for plate-making by dissolving a stencil plate in an acidic solution. However, these processes require their special solutions and had some problems from the stand points of safety and environmental pollution.
As a stencil printing plate, a heat-sensitive stencil plate has conventionally been known which is obtained by superposing a thermoplastic resin film on a porous substrate and adhering to each other. In this heat-sensitive stencil plate, there are some processes for plate-making, for example, (1) a process for plate-making by using a heat-generating device of a flash lamp, infrared lamp or others, superposing a hand-written manuscript or preliminarily prepared manuscript on a heat-sensitive plate, and melting and perforating a thermoplastic resin film by the generated heat from the device described above, (2) a process for plate-making by using a thermal head for generating a dotted heat corresponding to a letter image information converted into an electric signal, bringing a heat-sensitive stencil plate in contact with the thermal head, and melting and perforating the thermoplastic resin film.
However, since the processes for plate-making described above require a series of complicated processes for bringing a light-absorbed and heat-generated manuscript or thermal head in contact with a heat-sensitive stencil plate, conveying the heat to the thermoplastic resin film in the heat-sensitive stencil plate to melt the thermoplastic resin film, and subsequently perforate the thermoplastic resin film, there were some problems, for example, (1) a perforation failure is produced due to the incomplete contact between a thermoplastic resin film and a manuscript or thermal head for absorbing the heat; (2) an adhesion failure is produced due to the nonuniformity in contacting pressure of the thermal head, or shrinkage is produced in the heat-sensitive stencil plate; (3) a transfer failure of the heat-sensitive stencil plate occurs due to the melted material of the thermoplastic resin being adhered to the thermal head; (4) a printing failure is produced since the melted material is left in the perforated portion and the passage of the ink is prevented; and others.